Global warming of 1.5 degrees above pre-industrial levels will be catastrophic for almost all coral reefs, including those that scientists once hoped would act as refuges during climate change.
Only 0.2 per cent of coral reefs globally are likely to avoid frequent heat stress if temperatures warm, according to new research from an international team of universities, including James Cook University in Townsville.
James Cook University marine biologist Jodie Rummer at work on the Great Barrier Reef. She has witnessed previous bleaching and described it as “scary and disturbing”.Credit:Grumpy Turtle
This finding comes as the Great Barrier Reef is on the cusp of another mass coral bleaching event because of record-breaking ocean temperatures, with reports that scattered areas of coral off Townsville and Mackay are already showing signs of heat stress.
This is alarming because the potential bleaching would be occurring during a La Nina weather event, which traditionally brings cooler and cloudier weather, but reef temperatures are some of the warmest ever recorded.
Associate Professor Scott Heron, one of the study authors from James Cook University, said scientists used cutting-edge climate modelling to predict how much thermal exposure shallow-water coral reefs would experience around the globe.
Even thermal refuges, which experts assumed would be more able to endure warming oceans owing to factors such as the consistent upwelling of cool deep waters, would provide almost no protection to reef animals, the study found. It is published today in PLOS Climate.
Bleaching of the Great Barrier Reef near Heron Island in 2016. Credit:Eddie Jim
Dr Heron said “this means corals worldwide are at even greater risk from climate change than previously thought, especially as limiting warming to 1.5 degrees is looking increasingly unlikely”.
In the three months leading up to mid-December, heat stress at the Great Barrier Reef reached record levels.
Great Barrier Marine Park Authority chief scientist David Wachenfeld said “we are now two-thirds of the way through summer, there’s a quite reasonable accumulation of heat stress out there and the next four weeks are absolutely critical”.
“The weather that we see will very strongly influence the outcome of the reef.”
Ocean temperatures for most of the reef have been between 0.5 degrees and 1.5 degrees higher on average since the beginning of summer in most places, most of the time, he said.
While cyclones Seth and Tiffany and recent monsoonal rain did have some cooling effect, this hasn’t brought the reef back to average temperatures
There have been reports of minor coral bleaching in a range of places such as Cooktown, Townsville and Mackay that demonstrates the coral is showing early signs of stress, Dr Wachenfeld said.
“The thing that worries me when there is a severe impact to the Great Barrier Reef [is that] I always worry that people lose hope,” he said. “What the reef needs right now is the strongest possible action globally to reduce greenhouse gas emissions, with the strongest action to protect it locally.”
Last week the federal government promised to spend $1 billion on the reef over nine years, pledging new money for new technology, water management and coral seeding. Reef experts welcomed the additional funding, but said it would do nothing to save the reef from the existential threat of climate change
The Bureau of Meteorology says that December 2021 was, on average, the warmest December for the Great Barrier Reef since records began in 1900.
Above-median rainfall is predicted for much of February at Cape York and the Great Barrier Reef, and the extent of wind, cloud and rain will influence ocean temperatures.
Associate Professor Jodie Rummer witnessed coral bleaching in 2016 when the James Cook University reef expert was working on a project on the effects of climate change on reef fish at the Lizard Island research station, off Cooktown.
The water temperature was two or three degrees higher than normal, similar to the temperatures she was simulating in the laboratory to reflect what was expected in the middle of this century.
“It was scary and disturbing,” Dr Rummer said. “I grew up with these dreams of wanting to make my contribution to science and conservation … and to see this happening before my eyes in my lifetime has been really, really upsetting.”
The reef is an internationally significant tourist destination, which supports 64,000 jobs and contributes $6.4 billion annually to the economy. It suffered severe back-to-back bleaching that wiped out swathes of corals in 2016, 2017 and 2020.
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